Isotopic reconstruction of the African Humid Period and Congo Air Boundary migration at Lake Tana, Ethiopia
Isotopic reconstruction of the African Humid Period and Congo Air Boundary migration at Lake Tana, Ethiopia
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DOI：
10.1016/j.quascirev.2013.10.031
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发表时间：
2014-01-01
影响因子：
4
通讯作者：
Lamb, Henry
中科院分区：
文献类型：
--
作者：
Costa, Kassandra;Russell, James;Lamb, Henry
全新世早期到中期（12,000-5000年前）的非洲湿润期产生了巨大的生态和社会影响，包括植被和文明向“绿色撒哈拉”的扩张。虽然湿润期本身在整个北部非洲和赤道非洲都有很好的记录，但在观测到的湿润期时间和幅度的区域变化背后的机制仍然存在争议。本文提出了来自埃塞俄比亚塔纳湖（北纬12度，东经37度）15000年沉积物岩心的叶片蜡（δ d -蜡）的新的氢同位素记录，以深入了解非洲东北部非洲湿润期的时间、持续时间和强度。塔纳湖的d -蜡含量在-80‰之间。在距今13000 - 11500年（13-11.5 ka）之间，从富d到贫d的蜡质突然转变。大约在8.5-8 ka发生了类似的从缺d到富d的突然转变，随后在整个全新世晚期普遍富d。δ d -蜡的变化趋势与北半球夏季日晒变化相关，反映了AHP期间塔纳湖降水的增加；然而，塔纳湖从缺d到富d的转变比其他许多区域记录发生得更早（约8 ka， vs . 5 ka），而且在AHP期间，塔纳湖的缺d幅度也更大。我们将这种早期富集归因于西风来源（刚果盆地和大西洋）的水分减少，我们认为相对于东（印度洋）和北（红海和地中海）的水分，西风来源（刚果盆地和大西洋）的水分减少了d。我们的新记录强调了热带雨带的北移和刚果气界的东西移对非洲湿润期降水源和降水量的重要性。(C) 2013 Elsevier Ltd.版权所有。
The African Humid Period of the early to mid-Holocene (12,000-5000 years ago) had dramatic ecological and societal consequences, including the expansion of vegetation and civilization into the "green Sahara." While the humid period itself is well documented throughout northern and equatorial Africa, mechanisms behind observed regional variability in the timing and magnitude of the humid period remain disputed. This paper presents a new hydrogen isotope record from leaf waxes (delta D-wax) in a 15,000-year sediment core from Lake Tana, Ethiopia (12 degrees N, 37 degrees E) to provide insight into the timing, duration, and intensity of the African Humid Period over northeastern Africa. delta D-wax at Lake Tana ranges between -80 parts per thousand. and -170 parts per thousand, with an abrupt transition from D-enriched to D-depleted waxes between 13,000 -11,500 years before present (13-11.5 ka). A similarly abrupt transition from D-depleted to D-enriched waxes occurs ca 8.5-8 ka and is followed by generally D-enriched waxes throughout the late Holocene. Trends in delta D-wax covary with changes in Northern Hemisphere summer insolation and reflect increased precipitation at Lake Tana during the AHP; however, the transition from D-depleted to D-enriched waxes occurs earlier at Lake Tana (ca 8 ka, vs 5 ka) than in many other regional records, and the amplitude of D-depletion during the AHP is larger at Lake Tana as well. We attribute this early enrichment to a reduction of moisture derived from westerly sources (the Congo Basin and Atlantic Ocean) which we suggest are D-depleted relative to moisture sourced from the east (Indian Ocean) and the north (Red Sea and Mediterranean Sea). Our new record highlights the importance of both the northward migration of the tropical rain belt as well as east-west migration of the Congo Air Boundary to precipitation source and amount during the African Humid Period. (C) 2013 Elsevier Ltd. All rights reserved.